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What does it mean to conjugate a verb? how do you conjugate verbs in spanish?

Select the word from the list that best fits the definition tu madre espera que tú en casa a las ocho. hable hagan sepa estès escribamos

Achemist mixes 4 liters of one acid solution with 10 liters of a 40% solution, resulting in a 30% acid solution. what is the value of x, the acid concentration of the first solution